This invention relates in general to medical imaging and more particularly relates to the use in computed radiography (CR) of an elongated CR cassette for imaging elongated body regions, such as the full spine or the leg.
Conventional size radiographic image acquisition units are limited in size and unsuitable for imaging elongated body regions such as the full spine or the leg. The largest conventional radiographic film and radiographic computed radiography plates used in chest radiography are 35xc3x9743 cm. (14xc3x9717 in.). When it is necessary to obtain a radiographic image of a full spine or leg, several approaches have been used. If film/screen technology is used, either an extra long, non-standard radiographic film is used, or as disclosed in U.S. Pat. No. 3,774,045, issued Nov. 20, 1973, inventor Trott and U.S. Pat. No. 3,725,703, issued Apr. 3, 1973, inventor Bucky, cassette or cart is provided for holding a plurality of overlapping conventional sized film cassettes or packs. In the case of a special elongated film, the cost of the film and its processing is substantially greater than the cost of the conventional sized film. In the case of multiple film solutions, the films must be taped together to obtain the full length radiographic image. This introduces overlap and alignment problems.
Similar solutions have been proposed when computed radiography plates are used. Thus, U.S. Pat. No. 5,130,541, issued Jul. 14, 1992, inventor Kawai discloses a self enclosed CR unit using elongated CR plates that are exposed, read, erased and reused within the unit. U.S. Pat. No. 5,111,045 discloses a self enclosed unit using conventional sized CR plates that are exposed, read, erased and reused within the unit. When an elongated body region is imaged, first and second overlapping CR plates are positioned at the exposure station, exposed and then processed. Both of these solutions are disadvantageous in the use of an expensive, heavy, self-enclosed unit that is unsuitable for use when a patient is unable to use the unit due to physical disability or when admitted to a hospital emergency room, intensive care unit or surgical suite.
EP Patent application EPO 919856A1, published Feb. 6,1999, inventor Dewaile et al. discloses an assembly for recording a radiographic image of an elongated body including a plurality of CR cassettes holding conventional sized CR plates that are held in staggered arrangement so that the length of the staggered arrangement is equal to at least the length of the elongated body. After exposure, the CR plates are read individually and the read electronic images are stitched together to form the entire image of the elongated body. This technique is disadvantageous in requiring the use of a special assembly to hold the CR cassettes. U.S. Pat. No. 5,986,279, issued Nov. 16, 1999, inventor Dewaile, discloses an elongated CR cassette holding a plurality of overlapping or non-overlapping CR screens. After exposure, the CR screens are removed from the elongated cassette, put into xe2x80x9cnormalxe2x80x9d sized cassettes, and applied to a read out device that is able to read out normal sized cassettes. This technique is disadvantageous in the time and expense involved in loading and unloading the elongated cassette as well as in the subsequent handling of individual CR cassettes to enable CR screen readout.
It is also desirable that an effective and cost efficient process be provided to align read out sub-images for accurate composite image generation.
There is thus a need for a solution to these problems.
According to the present invention, there is provided a solution to the problems of the prior art.
According to a feature of the present invention, there is provided a storage phosphor cassette for use in recording radiographic images of elongated objects comprising: first and second storage phosphor plates having first and second length dimensions; a shell having first and second opposite open ends, a first assembly for detachably mounting said first storage phosphor plate in said shell from said first open end; a second assembly for detachably mounting said second storage phosphor plate in said shell from said second open end, wherein said first and second storage phosphor plates are mounted in said shell such that they form a substantially continuous storage phosphor composite for recording an elongated radiographic image; and an elongated ruler located on the inside or outside of said cassette, said ruler being x-ray translucent/opaque to produce an image of said ruler in said first and second storage phosphor plates.
The invention has the following advantages.
1. Radiographic images of an elongated object can be made in a single exposure using conventional size CR plates.
2. The CR plates are exposed to a radiographic image in the same plane, obviating the need for stacking multiple cassettes and performing complex corrections or multi-plane images.
3. The CR plates are not handled manually and are read automatically thus minimizing degradation of the CR plate and resultant image degradation.
4. A process is provided for aligning sub-images for accurate composite image generation.
5. The composite image can be constructed automatically without human intervention. The composite image construction software only requires a prior knowledge that a scoliosis/elongated body image should be generated. Providing to the image processing software the exam information is consistent with current CR image processing algorithms. In the prior art, a technologist is required to interact with the image processing software via a workstation user interface to select and sequence the images that are to be digitally stitched into a composite.
6. Embedded in the composite image is a human readable reference for distance that can be used by the radiologist or clinician for qualitative assessments, which provides absolute distance measurement and is invariant to image viewing methods.
7. Because the image is at most 2xc3x97 size of a standard 2500 pixelxc3x972000 pixel image, the composite image can be automatically routed and printed on a single sheet of film at full resolution using a standard 5Kxc3x974K laser printer, e.g., Kodak 2180 Laser Printer. However, the image will not be printed at true size.